A turbocharger is a type of forced induction system used with internal combustion engines. Turbochargers deliver compressed air to an engine intake, allowing more fuel to be combusted, thus boosting the horsepower of the engine without significantly increasing engine weight. Thus, turbochargers permit the use of smaller engines that develop the same amount of horsepower as larger, normally aspirated engines. Using a smaller engine in a vehicle has the desired effect of decreasing the mass of the vehicle, increasing performance, and enhancing fuel economy. Moreover, the use of turbochargers permits more complete combustion of the fuel delivered to the engine, which contributes to the highly desirable goal of a cleaner environment.
Turbochargers typically include a turbine housing connected to the exhaust manifold of the engine, a compressor housing connected to the intake manifold of the engine, and a center or bearing housing disposed between and coupling the turbine and compressor housings together. The turbine housing defines a generally annular chamber, consisting of a scroll or volute, which surrounds the turbine wheel and receives exhaust gas from an exhaust supply flow channel leading from the exhaust manifold of the engine. The turbine housing generally includes a nozzle that leads from the generally annular chamber, consisting of the scroll or volute, into the turbine wheel. The turbine wheel, in the turbine housing, is rotatably driven by an inflow of exhaust gas supplied from the exhaust manifold. A shaft rotatably supported in the center or bearing housing connects the turbine wheel to a compressor impeller in the compressor housing so that rotation of the turbine wheel causes rotation of the compressor impeller. The shaft connecting the turbine wheel and the compressor impeller, defines a line which is the axis of rotation.
Exhaust gas flows into the generally annular turbine chamber, consisting of the scroll or volute, through the nozzle, to the turbine wheel, where the turbine wheel is driven by the exhaust gas. The turbine wheel spins at extremely high speeds and temperatures. As the turbine wheel spins, the turbine extracts power from the exhaust gas to drive the compressor. The compressor receives ambient air through an inlet of the compressor housing and the ambient air is compressed by the compressor wheel and is then discharged from the compressor housing to the engine air intake. Rotation of the compressor impeller increases the air mass flow rate, airflow density and air pressure delivered to the cylinders of the engine via the engine intake manifold thus boosting an output of the engine, providing high engine performance, reducing fuel consumption, and environmental pollutants by reducing carbon dioxide (CO2) emissions.
The turbocharger center or bearing housing includes a bearing system that is used to support the shaft and keep the shaft spinning freely. The bearing system also aids in resisting radial and thrust loads created by the compressor and turbine wheels. Thrust loading is created by pressure differentials between the compressor and turbine housings. Thrust loads are imposed along the axis of the shaft and tend to push the shaft back and forth. Radial loads act perpendicularly to the axis of the shaft and are a cause of the back and forth shaft motion. A bearing system commonly used in turbochargers, typically consists of a journal bearing assembly that are cylindrical bearings which contain the radial loads and a thrust bearing assembly that is generally a flat circular disk which manages the thrust loads. Oil is used to keep rotating parts of the turbocharger from rubbing, preventing metal-to-metal contact, and decreasing friction. Each end of the shaft is sealed, at a location at which the shaft passes through the bearing housing, in order to limit contact between the bearing lubricant and the gas. If lubricant is allowed to leak into the hot gas path, it can vaporize and burn, causing the creation of harmful soot and increased emissions.
In order to properly lubricate the turbocharger and rotating parts, a reliable and clean supply of oil must be provided. If the oil supply is insufficient, drops too low, or becomes contaminated with debris, the bearing system operating temperatures are drastically increased, severely diminishing the hearing system lifetime, creating an environment where it is highly likely that the turbocharger may become damaged and may ultimately fail. However, excessive oil flow can result in increased oil leakage through the turbocharger shaft and seals. The flow of air and oil crossing the seals of the turbocharger can be a significant source of inefficiency, and in severe cases destructive to the operation of the turbocharger and engine air system.